Composite article and method for producing same



Patented. May 23, 1939 PATENT OFFICE OOMPOSI'I'E ARTICLE AND METHOD FORBRODUOING SAME William Hale Church and Dorothy It. Bateman, Bui'lalo, N.Y., asslgnors, by means assignments, to E. I. du Pont do Nemours aCompany, Wilington. Del, a corporation oi Delaware No Drawing.Application July 31, 1934, Serial 8 Claims.

This invention relates to the art of coating and it particularlypertains to the production of moistureproof, coated, non-fibrous,celluiosic wrapping tissues, in which the surface coating tenaciouslyadheres to or is anchored to the cellulosic base, even when the tissueis placed in direct contact with water or when used as a wrappingdirectly in contact with products containing large amounts of water ormoisture for prolonged periods of time.

Sheets or films of regenerated cellulose have been renderedmoistureproof by coating with a moistureprooflng composition comprisingin its preferred and common form a cellulose derivative, a wax orwax-like material, a blending agent and a plasticizer. These coatedsheets are very eflectivc as a wrapping material for products such asbread cake, candy, cigars or the like, which it is desired to maintainin substantially their original fresh condition without any change inmoisture content. Such sheets, however, are unsuited for use as awrapping material directly in contact with products having a very highwater or moisture content, such as butter, cheese, wet or frozeniish,ice cream or the like, when they are stored for appreciable andsubstantial periods of time, since under such conditions themoistureproof surface coating tends to loosen and/or flake off,impairing the moistureproof property of the wrapping material andproducing an unsightly appearance.

It is an object of the present invention to produce coated articles inwhich the coating is securely anchored to the base material.

It is a further object of the invention to produce articles having acellulosic base to which is securely anchored a surface coating.

A still further object of the invention pertains to the molstureproofingoi non-fibrous base material wherein the moistureproof coating issecurely anchored to the base.

.Another object of the invention comprises the production ofnon-fibrous, cellulosic wrapping tissues having a molstureprooiingcoating which is securely attached or anchored to the base even whensubjected to the action of substantial quantitles of water over longperiods oi time.

An additional object comprises the production of transparent, flexible,moistureproof material adapted for use as a wrappin tissue directly incontact with products having a high water or moisture content, which itis desired to maintain in substantially their original state,characterized in that the moistureprooflng coating, after drying, issubstantially permanently secured to Renewed August 4. i938 the base bymeans of a substantially insoluble synthetic resin.

Other objects oi the invention will appear hereinai'ter.

Various methods for applying the. principles of 5 the invention havebeen discovered, for example, the anchoring effect may be obtained by(A) applying the synthetic resins to the cellulosic base sheet from anaqueous solution containing either the individual compounds such asphenol and formaldehyde, which will condense to form the resin, orcontaining a water-soluble incompletely condensed, tacky or stickysynthetic resin, the resin being completely condensed or polymerized onthe base sheet to form the insoluble, non-tacky resin, the surfacecoating being subsequently applied; (B) by applying to the cellulosicbase sheet an anchoring coating. comprising a synthetic resin in whichthe condensation of the resin-forming compounds has reached anintermediate state in which the condensation product is still sticky andtacky and soluble in organic solvents, the resin being applied fromorganic solvent solution, the polymerization then being permitted tocontinue on the base sheet until the condensation product has reached atack-free and substantially insoluble form, the surface coating thenbeing applied; (C) by dissolving orrotherwlse distributing in thecellulosic solution fromwhlch the him is cast, e. g. viscose, materialswhich will be co-precipitated when the fllm is cast and which willsubsequently yield insoluble, tack-free resins, casting the film andthen applying the surface coating. Various ways of carrying out thesemethods will be described in detail below, it being understood that theexamples given are illustrative and are not intended to unduly limit thescope of the invention.

By the expression anchor or equivalent thereof used herein is'meant thesecuring of the suriace coating imposed on the base in such a way thatthe resulting product will withstand the deleterious eflect of water ormoisture and the surface coatlng will not loosen and/or flake oil fromthe base when the product is directly in contact with water or moisturefor appreciable and substantial periods of time, c. g. for a period ofseveral weeks or more.

For the purposes of this specification and claims, we definemoistureproof materials as those which, in the form of continuous,unbroken sheets or films, permit the passage 0! not more than 690 gramsof water vapor per 100 square meters per hour, over a period of 24hours, at approximately 39.5 0. plus or minus 0.5 0., the

relative humidity of the atmosphere at one side of the film beingmaintained at least at 98% and the relative humidity of the atmosphereat the other side being maintained at such a value as to give a humiditydiflerential of at least 95%.

Moistureproofing coating compositions are defined as those which, whenlaid down in the form of a thin, continuous, unbroken film applieduniformly as a coating with a total coating thickness not exceeding0.0005" to both sides of a sheet of regenerated cellulose of thicknessapproximately 0.0009", will produce a coated product which ismoistureproof.

For the purposes of experimental tests, especially for those materialsadaptable as coating compositions, moistureproof materials include thosesubstances, compounds or compositions which, when laid down in the formof a continuous, unbroken film applied uniformly as a coating with atotal coating thickness not exceeding 0.0005" to both sides of a sheetof regenerated cellulose of thickness approximately 0.0009", willproduce a coated sheet which will permit the passage therethrough of notmore than 690 grams of water vapor per 100 square meters per hour over aperiod of approximately 24 hours, at a temperature of 395 C. plus orminus 0.5 C. (preferably 39.5" C. plus or minus 025 C.), with a watervapor pressure diiferential of 50-55 mm. (preferably 53.4 plus or minus0.7 mm.) of mercury. For convenience, the number of grams of water vaporpassed under these conditions may be referred to as "the permeabilityvalue." An uncoated sheet of regenerated cellulose having a thickness ofapproximately 0.0009" will show a permeability value of the order of6900.

From the foregoing, it is apparent that under the conditions set forth,'a moistureproofed regenerated cellulose sheet is capable of resistingthe passage of moisture of water vapor therethrough at least ten timesas effectively as the uncoated regenerated cellulose sheet.

The objects of the invention are accomplished by the following inventionwhich, in one of its phases, contemplates a cellulosic base, a surfacecoating comprising essentially a cellulose derivative, and an anchoringagent comprising a synthetic resin applied to and/or incorporated in thecellulosic base either as an intermediate condensation product which isstill tacky and soluble in organic solvents or, alternatively, solublein water, or as a mixture of the water-soluble compounds which condensesubsequently to form the resin, the condensation reaction then beingpermitted to take place until the resin has completely polymerized to atack-free, substantially insoluble state.

A. Anchoring by means of synthetic resins introduced from aqueoussolution The preferred form of the invention, whereby an extremelyeffective anchoring of a surface film to a base film may beaccomplished, comprises applying the synthetic resin onto the base froman aqueous medium. In accordance .with this form of the invention, theaqueous solution to be applied to the base film comprises either asolution of the individual resin-forming compounds, for example, aphenol and an aldehyde, or, alternatively, an aqueous solution of anincompletely condensed synthetic resin which is still soluble in water,the intermediate resin, after deposition onto the base film, beingcapable, at

' elevated temperatures in the presence of a condensing agent orcatalyst, if desired, of condens- 7 and at temperatures not excessivelyhigh.

ing to form an insoluble, non-tacky resin. After applying theintermediate resin to the film. the film is then subjected totemperatures sufficiently high to cause the formation therein andthereon of the resin in a tack-free and insoluble state during thedrying of the ceiluiosic sheet.

Resins suitable for application to the nonfibrous base sheet, accordingto this method of the invention and having the characteristics desirablein an anchoring medium, are resins of the phenol-aldehyde andurea-aldehyde types.

Resins contemplated as suitable for application as coatings for thispreferred form of the invention are resins capable of rapid formation attemperatures under 200 6., preferably capable of formation in 5 minutesor less at temperatures C. or less, substantially insoluble andunaffected by water and organic solvents such as those employed insurface coating compositions, preferably substantially colorless atleast in very thin films which are preferably less than 0.0001" inthickness and formed by the reaction of substances which are themselvessufllciently watersoluble to yield aqueous solutions of the necessaryconcentration.

Combinations of resin-forming materials which may be employed in diluteaqueous solution to produce a suitable resin as an anchoring medium inor on the celluloslc sheet include meta-cresol and formaldehyde,resorcinol and formaldehyde, phloroglucinol and formaldehyde, orcinoland formaldehyde, phenol and formaldehyde, methyl-phloroglucinol andformaldehyde, resorcinol monomethyl ether and formaldehyde, preferablyin each instance with an alkaline condensing agent such assodiumhydroxide, potassium hydroxide, sodium carbonate or, in some cases, anamine like ethylene diamine; or a suitable aqueous solution may containurea, theourea, melamine, or other sufficiently water-soluble carbamideor cyanuric acid derivative and formaldehyde with an acidic or alkalinecondensing agent, preferably the former. Formaldehyde maybe replaced byother water-soluble and reactive aldehydes such ase acetaldehyde,glyoxal, or the like, in aqueous solutions of either phenolaldehyde oraldehyde-amino resin-forming materials. In most cases, however,formaldehyde is more satisfactory as reacting more readily with thephenol, carbamide or cyanuric acid derivative in question. Of course,phenolic compounds other than the ones herein named may be used inaqueous solutions designed to produce substantially insolublephenol-aldehyde resins in or on a non-fibrous cellulosic sheet, but thephenolic compounds mentioned have been found most suitable with respectto water-solubility and conversion to substantially insoluble resinsquickly It should also be noted that phenolic compounds having two ormore hydroxyl groups meta to each other react with aldehydes to producesubstantially insoluble resins much more quickly and at lowertemperatures than phenol itself, for example, or a polyhydric phenolwith two or more hydroxyl groups not meta to each other.

In introducing a urea-formaldehyde resin into or on the non-fibrouscellulosic sheet, it is much more convenient to employ in place of anaqueous solution of urea, formaldehyde and a condensing agent, anaqueous solution of dimethylol urea, which is a water-solublecondensation product of urea and formaldehyde formed in an alkalinemedium, with a condensing agent which will impart to the solution a pHbetween 3 and 5,

til

such as salicylic acid, gluconic acid, or ammonium thiocyanatc, forinstance.

In employing aqueous solutions of resin-torming materials, we preferdilute solutions, preferably of such concentration that the total weightor resin-iorming materials is between 1.5 and 3 per cent and the weightof condensing agent, it used, between 0.01 and 0 .15 per cent, although,of course, solutions more or less concentrated in resin-formingmaterials or condensing agent may be used 11' desired. In thesesolutions, a desirable molar ratio of phenol to aldehyde isapproximately 1 to 3 and a suitable ratio oi carbamide to aldehyde is 111101 of carbamide to 2-3 mols of aldehyde, although it is understoodthat these ratios may be varied in any desirable manner withoutdeparting from the essential procedure of forming in or on a non-fibrouscellulosic sheet a substantially insoluble resin by causing to react bymeans of elevated temperatures, preferably with a condensing agent,materials capable of forming the resin and introduced into or on thecellulosic sheet from their aqueous solution.

The term "carbamide, as used throughout the specification and. claims,is meant to include carbamide derivatives and derivatives of cyanuricacid.

As a base, this invention contemplates any smooth, dense, substantiallynon-porous, nonfibrous, cellulosic sheet, film or tubing precipitatedfrom an aqueous cellulosic dispersion or solution, or from a solution ofa cellulose ester or ether in an organic solvent or mixture of solvents.This includes sheets or films of regenerated cellulose, whetherprecipitated from solutions of viscose, cuprammonium, or any otheraqueous solutions or dispersions of cellulose, and also sheets or filmsof such cellulose esters and ethers as are precipitated from aqueoussolutions or dispersions, such as glycol cellulose, cellulose glycollicacid, methyl or ethyl cellulose of low alkyi content, cellulose phthalicacid and other similar cellulose products described by these terms; alsosheets or films of cellulose acetate, cellulose propionate, cellulosebutyratc, ethyl cellulose, benzyl cellulose or any other ester or etherof cellulose precipitated from a solution of the cellulose derivative inan organic solvent or solvent mixture. It is, of course, understood thatthis invention does not contemplate as a base cellulose esters or ethersin the stage of esterification or etheriflcation which renders themsoluble in the solvents employed in the surface coating to be applied.However, there are many degrees of est-erification or etheriiicationwith corresponding degrees of solubility in various solvents, and thisinvention does comprehend sheets or films of cellulose esters or ethersat stages of esterification or etherification in which they are solublein certain organic solvents or solvent mixtures and yet are insoluble inthe organic solvents employed in the surface coating solution. When anygiven coating composition is applied to such sheets or films, saidcoating composition will not penetrate therethrough and will normallyresult in asuriace coating.

In certain cases of coated materials, this invention also contemplatesas a base cellulosic threads or fibers, whether natural fibers such ascotton, linen, jute, ramie, hemp, or the like, or synthetic fibersprecipitated from aqueous cellulosic dispersions or solutions, or fromsolutions of cellulose derivatives in organic solvents. It will beunderstood, however, that the preferred form or the invention comprisesits application to non-fibrous cellulosic sheets or him: and thedetailed description of the invention will be so limited. a

As a surface coating this invention contemplates any flim-iormingcomposition, preferably a moistureproof composition, having a cellulosederivative base or a base consisting of an ether resin, a vinyl resin,rubber, a rubber-like material, rubber derivative, or product resultingfrom the chemical treatment of rubber, any of which bases may bemodified by the addition or blending agents, waxes or wax-likematerials, plasticizers, et cetera. Cellulose derivatives suitable foruse as a coating base include cellulose nitrate, cellulose acetate,ethyl cellulose, benzyl 'cellulose, or the like. By the term, etherresin" is meant a resin during the production of which ether linkagesare formed and resulting from the reaction of polyhydric phenols withaliphatic polyhalides, such as, for example, the resin formed by thereaction of dihydroxydiphenyl propane and B,B'-dichlorodiethyl ether inthe presence of alkali. Among the vinyl resins, we prefer a resincomposed of 60 per cent vinyl chloride and -i 0 per cent vinyl acetatealthough various other vinyl resins are suitable for use in coatingcompositions. As rubber-like materials, rubber derivatives or productsresulting from the chemical treatment of rubber may be mentionedthermoprene, a thermoplastic, unsaturated hydrocarbon derived fromrubber hydrocarbon, described in detail by H. L. Fisher in "Industrial &Engineering Chemistry, vol. 19, No. 12, page 1325, hydrogenated rubber,polymerized chloro- 2-butadiene-l,3, chlorinated rubber, those productsknown under the trade names "Pliolite" and "Plioi'orm, the reactionproducts of rubber and stannic chloride, ferric chloride, boronfluoride. chlorostannic acid, etc., described in detail by Thies andClifford in "Industrial and Engineering Chemistry, vol. 26, page 123, orthelike. The surface coating may be applied to the cellulosic material.from solution in organic solvents or from a melt, depending upon thenature of the cellulosic material to be coated and the composition ofthe coating employed. In the preierred form, for coated cellulosic sheetor film materials, the surface coating is a moistureproof coatingcomprising a cellulose derivative, a wax or wax-like material or othermoistureprooiing agent, a blending agent and a plasticizer, and isapplied from solution in organic solvents.

In order that the finished non-fibrous cellulosic sheet may be of thedesired softness, a softener such as glycerine may be incorporated inthe aqueous solution of resin-forming materials. Varying amounts ofsuitable dyes may also be added to the solutions The aqueous solution ofresin-forming materials may be applied to the non-fibrous cellulosicsheet by dipping or immersing the sheet in the solution, by brushing orspraying the solution on the sheet or by applying it to the sheet byrollers or by any other convenient means. Moreover, the solution may beapplied either to the cellulosic sheet in the gel condition, that is,after the same has been coagulated and at least partially regeneratedbut before being dried, or to the finished, dry cellulosic sheet. In anycase, after the application of the aqueous solution of resin-formingmaterials to the cellulosic sheet, the excess solution is removed fromsaid cellulosic sheet by squeeze rolls or any known means, preferably tosuch an extent that an amount of III weight of the cellulose remains inthe cellulosic sheet. The amount of substantially insoluble resinpresent in or on the finished dry cellulosic sheet depends upon theconcentration of the aqueous solution of resin-forming materials usedand upon the amount of this solution removed from the sheet by squeezerolls or other means prior to the drying of the sheet, but, in thepreferred form of this invention, ranges from2 to 12 per cent of theweight of the sheet, although it may be desirable for certain purposesto have present in or on the cellulosic sheet amounts of resin greateror less than those included within these limits.

The amount of heat required to convert the resin-forming materials,applied to the cellulosic sheet from an aqueous solution, to asubstantial ly insoluble resin varies, of course, with the individualresin and the materials employed to produce it. From the standpoint ofconvenient operation and effect upon the cellulosic sheet, it is usuallydesirable to effect the formation of the resin in a comparatively briefperiod of 5 minutes or less at temperatures under 100" C. It ispossible, however. to vary the time and temperature rather widely tosuit the requirements of special resins without unfavorably affectingthe quality of the cellulosic sheet. Temperatures very much under 100.sometimes as low as 40 to 50 C., are oftai sufficient and desirable tocause resinformation in or on the sheet when a period of time longerthan 5 minutes is employed. Moreover, a temperature much higher than 100(3., even as high as 180' C. can be applied for a very brief interval toa cellulosic sheet wet with an aqueous solution of resin-formingmaterials to bring about the formation of the desired substantiallyinsoluble resin without damaging the cellulosic sheet. The necessaryheat may be applied by bringing the cellulosic sheet into contact withheated dryer rolls or other heated surfaces or by leading the sheetthrough a heated atmosphere or in any other manner. In some cases, wherethe formation of the resin from the materials used in the aqueoussolution is slow and it is undesirable to employ a high temperature tospeed up the resin-formation, the reaction can be completed in the shorttime and at the desired only moderately elevated temperature by allowingthe solution of resin-forming materials to stand or "age for severalhours before applying it to the cellulosic sheet. Presumably, at least,the initial condensation of the resin-forming materials takes place inthe solution before its introduction to the cellulosic sheet and therebyshortens the time required for completing the reaction to form asubstantially insoluble resin in or on said sheet.

In its preferred and simplest form for producing non-fibrous cellulosicsheet or film materials, capable of securely anchoring a surfacecoating, this invention contemplates applying the dilute aqueoussolution of resin-forming materials to the cellulosic sheet in the gelcondition directly on the casting machine, as, for example, in themanufacture of regenerated cellulose sheeting. This can be doneconveniently by dissolving the resin-forming materials in the desiredamounts directly in the bath commonly used to provide a softeningtreatment and containing the aqueous solution of glycerine or othersoftener for the cellulosic sheet, allowing the gel sheet to be ledthrough said bath and subsequently dried in the usual manner. Theresulting sheet can then be 9,109,007 solution equal to between 3 and 4times thecoated with a moistureproof surface coating which will remainanchored to the sheet for a period of days or even weeks even in directcontact with water or moisture.

It will be apparent from the foregoing that this invention constitutes amarked departure from and improvement over previous processes forproducing moistureproof non-fibrous cellulosic sheets in which themoistureproof surface coating firmly adheres or is anchored to thecellulosic sheet even in direct contact with water or moisture. Thisprocess is simple, eliminating the inconvenience and expense of twocoating operations and requiring no additional equipment since theanchoring medium consisting of a substantially insoluble resin resultsfrom treating the cellulosic sheet with an aqueous solution ofresinformlng materials during the regular process for producing thecellulosic sheets. Moreover, the finished sheet, containing asubstantially insoluble resin therein or thereon, whether before orafter the application of a surface coating. is completely odorless.Furthermore, cellulosic sheets having a substantially insoluble resinpresent therein or thereon by reason of the treatment described by thisinvention are capable of retaining extremely well a surface coating witha cellulose derivative base or a base consisting of an ether resin, avinyl resin, rubber, a rubber-like material, rubber derivative, orproduct resulting from the chemical treatment of rubber (preferably amoistureproof surface coating). These surface coatings adhere or anchortenaciously to such cellulosic sheets even in direct contact with waterfor periods of weeks and are very suitable for use as a wrapping indirect contact with products having a high moisture or water contentsuch as butter. cheese, wet or frozen fish, ice cream or the like. Inaddition, non-fibrous cellulosic sheets containing therein or thereon asubstantially insoluble resin, according to this invention, have varioususes in themselves without the application of a surface coating. Byreason of the unique surface which they possess. for instance, they areparticularly adapted for certain types of printing and embossing and forvarious other uses which will at once suggest themselves. Moreover, thisinvention supplies a method of laminating together non-fibrouscellulosic sheets. Two or more non-fibrous cellulosic sheets wet with anaqueous solution of resinforming materials such as described by thisinvention can be caused to adhere very firmly by superimposing them onesheet upon the other and drying them thus under pressure at elevatedtemperatures sufllcient to cause the formation of the substantiallyinsoluble resin.

The following examples illustrate the anchor ing of a coating to a baseby the use of a solution of resin-forming components.

Example L-A sheet of regenerated cellulose in the gel condition whichhas been cast from viscose. desulfured, bleached and washed free fromimpurities in the usual manner in the casting machine and is ready forthe softening treatment, is led through an aqueous glycerine bath whichin addition to 4% per cent by weight of ghrcerine normally used forsoftening also contains one per cent by weight of resorcinol, 2 per centby weight of commercial formaldehyde (that is, 0.8% H200) and 0.02 percent by weight of sodium hydroxide, which solution has been allowed toage at room temperature for 12 hours or more before using. The sheet ofregenerated cellulm is in contact with the aqueous solution ofglycerine, resorcinol and formaldehyde for from 10 to 20 seconds, afterwhich the excess solution is removed from the sheet by means of squeezerolls which reduce the water content of the sheet to between three andfour times the weight of the cellulose, after which the sheet ofregenerated cellulose, wet with the solution of resin-forming materialsand glycerine, is ready to be dried. During the drying, water is removedfrom the sheet of regenerated cellulose and the resin-forming materialsreact under the influence of the heat employed for the drying to form asubstantially insoluble resin in or on the sheet.

Drying may be carried out according to the usual method for dryingregenerated cellulose sheeting on the casting machine by bringing thesheet directly from the squeeze rolls into contact with heated rolls anddrying the sheet at temperatures between 60 and 90 C. However, there maybe a tendency for the substantially insoluble resin, formed by thereaction of the resinforming materials, to be deposited on the dryerrolls as they become wet with the solution of resin-forming materialsfrom the wet cellulosic sheet passing over them. This deposit of resinmay flake off from time to time on the fresh cellulosic sheeting passingover the rolls, thereby imparting a faintly mottled appearance to thedry uncoated sheet.

Therefore, in this preferred example the regenerated cellulose sheet wetwith the solution of resin-forming materials and glycerine, afterpassing through the squeeze rolls and before coming into contact withthe dryer rolls is first given a preliminary partial drying out ofcontact with any surface by passing the sheet through air heated to anelevated temperature by means of a suitable arrangement of gas burnersor electric heaters, whereby the moisture content of the sheet isreduced to any desired extent, for instance, from /3 to /2 its initialwater content before coming in contact with the dryer rolls. Thepartially dried cellulosic sheet is then led over the heated rolls ofthe casting machine in the usual manner to complete the drying operationand to complete the formation of the substantially insoluble resin in oron the sheet.

The resulting sheet of regenerated cellulose with a substantiallyinsoluble resin therein or thereon may be rehumidified if necessary tobring it to the desired moisture content and is then coated with amoistureproofing composition of the following formula:

Per cent Nitrocellulose 6.44 Gum dammar 2.17 Dibutyl phthalate 2.40Paraflin (M. P. 60-6l C 0.52 Zinc stearate 0.17 Ethyl acetate 55.85Toluene 28.70 Ethanol 3.59 Acetone 0.15 Benzene 0.01

The sheet is passed through the moistureproofing composition, the excessof which is removed by scraping or any suitable means and the coatedsheet is dried at a temperature above the melting point of the wax,after which the finished, coated sheet may be again conditioned to bringit to the desired moisture content. The resulting product is a coatedsheet of regenerated cellulose which is transparent, flexible, odorlessand moistureproof, and to which, by reason of the presence in or on thecellulosic sheet of a substantially insoluble resin, the moistureproofsurface coating adheres or is anchored very tenaciously even when thesheet is in direct contact with water or is used as a wrapping directlyin contact with products containing large amounts of water or moisture,such as butter, cheese, wet or frozen fish, ice cream, or the like, forvery substantial periods of time.

Example II A sheet of regenerated cellulose in the gel condition whichhas. been cast from viscose, desulfuted, bleached, and washed free fromimpuritiesin the usual manner on the casting machine and.is ready forthe softening treatment, is led through an aqueous glycerine bath which,in addition to /2% by weight of glycerine, which is present forsoftening purposes, also contains 3 per cent by weight of dimethylolurea and 0.1 per cent byweight of salicylic acid, and which has beenallowed to stand for 48 hours at room temperature before using. Thesheet of regenerated cellulose is allowed to remain in contact with theaqueous solution of glycerine and dimethylol urea for from 10 to 20seconds after which the excess solution is removed from the sheet bymeans of squeeze rolls so that the water content of the sheet is reducedto between three and four times the weight of the cellulose. Theceliulosic sheet wet with the aqueous solution of glycerine anddimethylol urea is then dried according to the usual procedure fordrying regenerated cellulose sheeting by passing it over the heateddryer rolls of the casting machine. In this case, however, thetemperature of the dryer rolls is kept below 0., preferably between 40and 50 C. After drying the cellulosic sheet is conditioned if necessaryto bring it to the desired moisture content and is then coated with amoistureproofing lacquer of the following composition:

Per cent Nitrocellulose 6.44 Gum dammar 2.17 Dibutyl phthalate 2.40Parafiin (M. P, 60-61 C 0.52 Zinc stearate 0.17 Ethyl acetate 55.85Toluene 28.70 Ethanol 3.59 Acetone 0.15 Benzene 0.01

The sheet is passed through the moistureprooiing composition, the excessof which is removed by scraping or other suitable means, and the coatedsheet is dried above the melting point of the wax, after which thefinished sheet may be conditioned again to bring it to the desiredmoisture content. The resulting coated sheet of regenerated cellulose isflexible, transparent, odorless, colorless and moistureproof, andretains its moistureproof surface coating very tenaciously forappreciable and substantial periods of time even in direct contact withwater or as a direct wrapping for products containing large amounts ofwater or moisture.

Example III.-A sheet of regenerated cellulose treated with an aqueoussolution of glycerine, resorcinol, formaldehyde, and sodium hydroxideand dried according to the procedure in Example I and ready for theapplication of the surface coating, is coated with a moistureproofingcomposition comprising a solution of ethyl cellulose, paraflin, ablending agent and a plasticizer.

Example IVFA sheet of regenerated cellulose treated with an aqueoussolution of glycerine, resorcinol, formaldehyde and sodium hydroxide anddried according to the procedure in Example I and ready for theapplication of the surface coating is coated with a moistureprooflngcomposition comprising a vinyl resin (60% vinyl chloride and 40% vinylacetate), a wax and a plasticizer.

Example V.--A sheet of regenerated cellulose treated with an aqueoussolution of glycerine, resorcinol, formalderyde and sodium hydroxide anddried accordang to the procedure in Example I, and ready for theapplication of the surface coating is coated with a compositioncomprising essentially the ether resin prepared by condensingdihydroxydiphenyl propane and B, B-dichlorodlethyl ether in alkalinesolution, and a wax.

Example VL-A' finished or dry sheet of glycol cellulose is immersed inan aqueous solution containing 0.75% phloroglucinol, 1.5% commercialformaldehyde, 87%, (that is, 55% H260). and 0.015% sodium hydroxide. Theexcess solution is removed from the sheet which is dried at an elevatedtemperature, preferably between 70 and 90 C., and the resulting driedsheet is coated with a composition comprising essentially Pliolite and awax.

Example VII.-A sheet of cellulose acetate is immersed in the aqueoussolution described under Example VI, dried and coated with amoistureprooi' coating comprising, essentially, the ether resin formedby the reaction of dihydroxydlphenyl propane and B,B'-dichlorodiethylether in alkaline solution, and a wax.

Example VIII.--A sheet of regenerated cellulose is passed through anaqueous solution containing one per cent by weight of m-cresol, 2 percent by weight of commercial formaldehyde (37%) and 0.02 per cent byweight of sodium hydroxide which has been allowed to stand for 48 hoursat room temperature before using. The excess solution is removed and thesheet dried almost completely at 90 C., then subjected to a very briefheating of 5 seconds, or preferably less, at a temperature of 180 C.,after which the sheet is cooled, humidified, and coated with amoistureprooflng composition comprising a solution of nitrocellulose,paramn, gum damar and dibutyl phthalate.

B. Use of soluble synthetic resins deposited from a non-aqueous solutionAn alternative method of anchoring a surface coating to a cellulosicbase can be effected by applying to the base a solution in an organicsolvent of an intermediate, tacky, or sticky, incompletely condensed orpolymerized synthetic resin, and subsequently completing thecondensation thereof to obtain a tack-free, substantially insolubleresin and then aplying the surface coating.

This form of the invention contemplates the use of base sheets, films,or tubing, such as have been described under A above.

The surface coating which may be used in accordance with this method iscapable of wide variation, for example, the coating may comprise acellulosic derivative base such as cellulose nitrate, cellulose acetate,ethyl cellulose, benzyl cellulose, or the like, which may be modified asdesired by the addition of blending agents, waxes, plasticizers, etc.Preferably, this invention contemplates 9. molstureproofing coatingcomprising in the preferred and common form a cellulose derivative, awax or wax-like material, a blending agent and a plasticizer. Forfurther variation in the character of the surface coating, see the dis-*cussion under "A".

In accordance with this alternative method, an undercoat of a syntheticresin is applied to the lmse from a solutoin in an organic solvent ormixture of solvents, the resin which is dissolved in the solution beingsticky or tacky, only partially condensed, polymerized or hardened, andbeing capable after deposition on the base sheet or film of beingcompletely condensed, polymerized, or hardened to a substantiallyinsoluble, tack-free form under the influence of heat and, if desired,in the presence of a catalyst.

We prefer to use for the anchoring undercoat partially condensed,polymerized or hardened synthetic resins which condense, polymerize orharden completely to a tack-free, substantially insoluble stage inextremely thin coatings, preferably less than 0.0001 inch in thickness,in a period of a few minutes at an elevated temperature preferably notexceeding 125 degrees 0., and it is desirable that the period be fiveminutes or less and the temperature be between 90 degrees and '1 degreesC. However, different resins will require different conditions and thetime and temperature may be varied according to the nature of theparticular resin used. Thus, for instance, a longer time at a lowertemperature may be employed to effect the desired result with a givenresin which in a shorter time would require a much higher temperature.It is, of course, understood that any of the well-known catalysts may beused with the partially condensed, polymerized or hardened resin toaccelerate its conversion to a final hardened, substantially insolubleform on the cellulosic sheet.

of the partially condensed, polymerized or hardened resins available, weprefer to use those with at least a fair degree of flexibility in orderto obtain undercoats which do not form visible cracks on the cellulosicsheet when it is creased or crinkled. It is often impossible, however,successfully to use resins which are commonly regarded as somewhatbrittle since for the purposes of this invention they are applied to thecellulosic sheet in such extremely thin layers that they flex with thesheet whereas thicker layers, of several ten-thousandths of an inchthickness, for example, would crack visibly if sharply bent. It is alsopreferable to employ for the anchoring undercoat partially condensed,polymerized or hardened synthetic resins which are substantiallycolorless in films of several ten-thousandths o1 an inch thickness orless and which are substantially odorless after having been condensed,polymerized or hardened and which are substantially free from dryingoils, drying oil acids or other drying oil derivatives.

As has been stated, the synthetic resin undercoat is usually extremelythin, preferably less than 0.0001 inch in thickness, being often as thinas 0.00001 to 0.00003 inch in thickness, so that the thickness of theresin-coated cellulosic sheet is not appreciably greater than that ofthe original sheet. To obtain resin undercoats of the requisite degreeof thickness, the partially condensed, polymerized or hardened syntheticresin may be applied from solution in a suitable solvent or mixture ofsolvents, such as acetone, ethanol, butanol, ethyl acetate, benzene,toluene, amyl acetate or the like. The resin solution may be of anysuitable consistency as determined by the apparatus employed and thethickness of the coating desired. In practice, solutions containingbetween 5 and per cent solids have been found convenient. Application ofthe resin solution to the cellulosic sheet may be made by immersing thesheet in the solution or by brushing or spraying the solution on thesheet or by applying the solution to the sheet by rollers or any otherconvenient means," after which the coating is smoothed and the excessremoved in any suitable manner.

The partially condensed, polymerized or hardened synthetic resinssuitable for use as an anchoring undercoat according to this alternativeform of the invention are not limited to the phenol-aldehyde resinsexclusive of all other types (although the phenol-aldehyde type ispreferred), but rather include resins of any type which answer therequirements of being capable of application to the cellulosic sheet ina. soluble, tacky, partially condensed, polymerized or hardened stageand of subsequent further complete condensatlon, polymerization orhardening to a final tack-free, substantially insoluble form on thesheet.

As specific resins suitable for use as anchoring undercoats according tothis invention may be cited certain phenol-formaldehyde resins knownunder the trade name "Durez" and also a resin formed by the interactionof dihydroxy-diphenylpropane and formaldehyde.

If for any reason it is desired to modify the characteristics of anyspecific partially condensed, polymerized, or hardened synthetic resinor of the anchoring undercoat which said resin forms on the cellulosicsheet, for example with respect to flexibility, hardness or color,certain other materials may be combined with the synthetic resin inquestion. These include natural resins and resirr'acids, such as, forexample, rosin and hydrogenated rosin, other synthetic resins, oils andoil acids, fats, waxes and wax-like materials, drying oils and dryingoil acids. dyes or the like. These materials may be combined with thepartially condensed, polymerized or hardened synthetic resin either byaddition along with the other ingredients during the preparation of theresin itself or by addition to the solution of said resin in organicsolvents after it has reached the partially condensed, polymerized orhardened stage and is ready for application to the cellulosic sheet. Itis to be clearly understood, however, that in the case of additions ofdrying oils or drying oil acids to the synthetic resins, the anchoringefi'ect depends upon the completion of the condensation, polymerizationor hardening of the partially condensed, polymerized or hardenedsynthetic resin to the final tack-free, substantially insoluble form onthe cellulesic sheet. It is also to be noted that if the addition to thesynthetic resin undercoat is a wax or wax-like material there resultsafter the completion of the condensation, polymerization or hardening ofthe synthetic resin on the cellulosic sheet, a coating of the resinwhich not only is firmly anchored to the cellulosic sheet even in directcontact with water or moisture but which also exhibits mois'tureproofness.

The following examples illustrate the anchoring of films by the use of asolution of a soluble resin:

Example IX .-The resin to be employed as the anchoring intermediatecoating or undercoat is prepared by condensing dihydroxydiphenyl-propaneand formaldehyde in alkaline solution at room temperature and isolatingthe viscous liquid resulting upon acidification of this solution. For

example, one molar equivalent of dihydroxydiphenyl-propane (M. P. 157C.) is dissolved in an aqueous alkaline solution containing 2 molarequivalents of sodium hydroxide, 3.25 molar equivalents of commercialformaldehyde (37%) are added and the clear solution allowed to stand fortwo days at room temperature. The mixture is then acidified and theviscous, practically colorless liquid which separates is washedacid-free and the water removed in a vacuum oven. This viscous liquid isa resin which at this stage is only partially condensed, polymerized orhardened and which requires additional heating to complete itscondensation, polymerization or hardening to a. tack-free, substantiallyinsoluble form. It is now dissolved in ethyl alcohol to give a solutionwhich will contain from '7 per cent to 33 per cent resin depending uponthe type ofcoating to be employed.

A coating of this ethyl alcohol solution of partially condensed,polymerized or hardened resin is applied to a finished sheet ofregenerated cellulose by passing the sheet through the solution,removing the excess by means of a suitable scraping mechanism to such anextent that the dried resin coating on the sheet will not exceed 0.0001inch in thickness, and thereafter drying the coated sheet at 110 C.until all the solvent has been removed from the sheet and the resincoating has become hard and tack-free and substantially insoluble. Theresin-coated cellulosic sheet is then cooled and rehumidifled to thedesired moisture content, after which the moistureproof surface coatingis applied by passing the cellulosic sheet through the moisture-proofingbath, removing the excess by means of a suitable scraping mechanism anddrying at a temperature above the melting point of the wax in themoistureproofing composition. After drying, the moistureproof coatedcellulosic sheet is again cooled and reconditioned to the desiredmoisture content. The moistureprooflng bath used in this example has thefollowing composition:

Per cent Nitrocellulose 5.21 Gum dammar 3.22 Dibutyl phthalate 2.30Paraflin (M. P. 61 C.) 0.88 Zinc stearate 0.10 Ethyl acetate 45.76Toluene 35.63 Ethanol 6.23 Acetone 0.67

The moistureproof sheet of regenerated cellulose produced by thisprocedure is transparent, flexible, odorless and colorless and retainsits moistureproof surface coating tenaciously even in direct contactwith water or moisture for prolonged periods of time so that it isadmirably suited for use as a wrapping material employed directly incontact with products containing large amounts of water or moisture suchas butter, cheese, wet and frozen fish, ice cream or the like, even whenthese products are to be stored for appreciable periods of time.

Example X .Riegenerated cellulose sheet material is coated with a 15 percent ethanol solution of a commercial product marketed under thedesignation Durez Serial No. 1622-R-2" which product is essentially apartially set up phenol: formaldehyde resin advanced in itspolymerization or condensation only to a stick or tacky stage. Afterbeing passed through the solution the cellulosic sheet is freed ofexcess solution by scraping or any convenient means so that the resincoating remaining on the sheet after drying will not exceed 0.0001 inchin thickness and is thereafter dried for several minutes at C. until theethanol has been volatllized and the resin has been converted to atack-free, substantially insoluble condition. The resin-coatedcellulosic sheet is then cooled and rehumidifled to the desired moisturecontent, after which it is coated with a moistureproofing compositioncomprising a solution of ethyl cellulose, a wax, a blending agent and aplasticizer, and, after removing the excess coating solution by suitablemeans, dried at a temperature above the melting point of the wax in themoistureprooilng composition, cooled and again rehumidified to thedesired moisture content.

The resulting moistureproof cellulosic sheet is transparent, flexible,odorless and colorless and its moistureproof surface coating is sosecurely anchored to the basic cellulosic sheet by virtue of theimmediate coating or undercoat of synthetic resin that said mostureproofcellulosic sheet can be very successfuly used in direct contact withwater or moisture. Moreover, the process described in the above exampleemploys synthetic resins which are easily reproducible with desiredcharacteristics.

0. Anchoring by means of synthetic resins dissolved or otherwisedistributed in the cellulosic film-forming solution It has furthermorebeen discovered that an effective anchoring of a coating to a cellulosicbase film may be accomplished by incorporating in the liquidfilm-forming material from which the base is cast, for example, in theaqueous alkaline cellulose xanthate solution used for the casting ofregenerated cellulose wrapping tissues by the viscose process,alkali-soluble, incompletely condensed or polymerized synthetic resinswhich are subsequently precipitated simultaneously with the cast sheet.In addition to incorporating a synthetic resin in the cellulosic sheetin the aforesaid manner, the resin-containing non-fibrous cellulosicsheet may also be treated with an aqueous solution of a substancecapable of further polymerization on heating or oi inter-action with theincompletely condensed or polymerized synthetic resin in the cellulosicsheet or of liberating formaldehyde or capable of two or of all of thesefunctions. After drying, the cellulosic sheet is ready for theapplication of the surface coating, preferably a moistureproof coating,in the usual manner. The process may be directly applied to existingequipment used in the manu facture of cellulosic sheets.

Carrying out this modification of the invention, in its preferred form,there will be produced an article comprising a cellulosic base, a,surface coating consisting essentially of a cellulose derivative or anether resin, and an anchoring medium comprising a synthetic resindispersed throughout the cellulosic base, and precipitated with it, froman aqueous, alkaline cellulosic dispersion or solution.

As a base this invention contemplates any smooth, dense, non-fibrous,cellulosic sheet or film precipitated from an aqueous alkalinecellulosic dispersion or solution. By this, we include sheets or filmsof regenerated cellulose and of such cellulose esters and ethers as areprecipitated from aqueous solutions or dispersions, such as glycolcellulose, cellulose glycollic acid, methyl cellulose and ethylcellulose, cellulose phthalic acid and other similar cellulose productsdescribed by these terms. When any given coating composition is appliedto such cellulosic sheets or films, the coating composition will notpenetrate therethrough and will normally result in a surface coating.

The surface coating applied to the synthetic resin-containing base, inaccordance with this form of the invention, may be of the same characteras has been discussed for the surface coating under A above.

As an anchoring medium the instant invention contemplates anyalkali-soluble, acid-insoluble, incompletely c'o densed or polymerizedsynthetic resin which as been dispersed uniformly throughout thecellulosic sheet by dissolving it in the aqueous, lkaline cellulosicsolution or dispersion from which the sheet is to be cast and thereafterprecipitated in and simultaneously with the cellulosic sheet by means ofthe acid precipitating bath. Resins of the phenol-aldehyde and polybasicacid-polyhydrlc alcohol types (commonly known as Glyptals") have beenfound particularly suitable for use as anchoring media in this manner.In addition to alkali-solubility and acid-insolubility, it is desirablethat the resin to be incorporated in the cellulosic sheet be capable offurther condensation or polymerization during the drying of thecellulosic sheet and that it be sufficiently condensed or polymerizedthat after the drying of the cellulosic sheet at elevated temperaturesit does not impart a sticky feel to the dry cellulosic sheet containingit. It is also desirable that the resins used in the practice of this]invention be substantially colorless, at least in very thin films. Asspecific resins which when incorporated in the cellulosic sheet bydissolving them in the aqueous alkaline cellulosic solution ordispersion from which the sheet is to be formed, impart to said sheetthe property of securely anchoring a surface coating may be mentionedphenol-formaldehyde or resorcinol-formaldehyde resins in suitable stagesof condensation or polymerization, resins formed by the condensation ofdihydroxydiphenyl propane and formaldehyde in alkaline solution, andpolybasic acid, polyhydric alcohol resins such as. for example, thecondensation product of glycerol, glycol, and adipic acid.

The resin to be employed as an anchoring medium is either added to theaqueous alkaline cellulosic solution or dispersion-directly, preferablyin finely divided form if it is a solid, and stirred until completelydissolved in the cellulosic solution or dispersion, or the resin may befirst dissolved in dilute sodium or ammonium hydroxide and the resultingalkaline solution of resin added to the cellulosic solution ordispersion with thorough mixing. Any desired amount of resin may beincorporated in the cellulosic sheet although from 5 to 25 per cent byweight of resin on the basis of the total solids in the sheet issufficient to give satisfactory anchorage. Moreover, amounts of resin inexcess of 25 per cent by weight of the solids in the finished sheetoften result in a somewhat weakened and less flexible sheet.

After the resin has been dissolved and well mixed in the aqueousalkaline cellulosic solution or dispersion, the cellulosic sheets arecast, coagulated, regenerated, washed and bleached, in the usual manner,softened if desired and dried at elevated temperatures, preferably notabove 110 C.

If it is desired to obtain still more permanent (ill anchorage of thesurface coating to the cellulosic sheet than is obtained by theincorporation of a resin in the cellulosic sheet containing thesynthetic resin dispersed therein, after being bleached and washed freeof impurities but before being dried, may be further treated by passingit through an aqueous solution of a compound capable on heating ofpolymerizing further or of inter-acting with the incompletely condensedor polymerized resin in the sheet or of liberating formaldehyde or oftwo or all of these functions. Thus dilute aqueous solutions ofdimethylol urea. monomethylol urea, hexamethylenetetramine,water-soluble condensation products of thiourea and formaldehyde orcyanuric acid and formaldehyde and many similar compounds may beemployed to good advantage. These compounds may be employed in aqueoussolutions of widely varying concentrations, limited, of course, by theirsolubility, but dilute solutions of from i to per cent by weight andpreferably of 2 to 4 per cent by weight are very suitable. If a softenerfor the cellulosic sheet is to be used, such as glycerine, for example,it may very conveniently be incorporated in the aqueous solution underdiscussion and be applied to said sheet simultaneously with thewater-soluble compound designed to improve anchorage. It is probablethat such water-soluble compounds as dimethylol urea,hexamethylenetetramine, water-soluble thiourea or cyanuric acid resinsor the like still further improve the anchorage of cellulosic sheetscontaining incompletely condensed or polymerized synthetic resinstherein by reason of their ability to liberate formaldehyde which mayreact with the resin in the sheet or by reason of their own ability tocondense or polymerize further which makes possible interaction with theresin in the cellulosic sheet. In either case the result would be asubstance on the surface of the cellulosic sheet chemically bound to theresin dispersed throughout the sheet. After the application of suchaqueous solution of a substance capable on heating of liberatingformaldehyde, further condensing or polymerizing, or of interacting withthe resin in the cellulosic sheet or of two or all of these functions,the excess solution is removed from the sheet by squeeze rolls or others table means so that the amount of solution remaining in the sheet isbe tween 3 and 4 times the weight of the sheet and the sheet is thendried at an elevated temperature, preferably under 110 C. in any desiredmannet.

The dried non-fibrous cellulosic sheet containing therein a syntheticresin incorporated as described according to this last-named alternativemethod, with or without having been subsequently treated prior to thedrying with an aqueous solution of a compound capable on heating ofestablishing a chemical union with the resin in the cellulosic sheet, isthen ready for the application of a surface coating, preferably amoistureproof surface coating, and is capable of anchoring said coatingfor substantial periods of time even when directly in contact with wateror moisture.

From the foregoing, it will be apparent that this invention constitutesa marked departure from, and improvement over, previous processes forproducing moistureproof non-fibrous cellulosic sheets in which themoistureproof surface coating firmly adheres to the cellulosic sheeteven in direct contact with water or moisture. This process is simplerand less expensive in operation. By adding the anchoring material to theaqueous alkaline cellulosic solution or dispersion before the cellulosicsheet is cast, the expense and inconvenience of two coating operationsare eliminated and a non-fibrous cellulosic sheet ready for the surfacecoating and capable of anchoring it is produced on the regularmachinery, as for example by the usual process for manufacturingregenerated cellulose sheets, without any additional equipment or changein procedure. The optional application to the resin-containingcellulosic sheet, prior to drying, of an aqueous solution of a substancecapable at the elevated temperature employed to dry the sheet of furthercondensation or polymerization. of interacting with the incompletelycondensed or polymerized resin in the cellulosic sheet, of liberatingformaldehyde or of two or all these functions. may be carried out in oneof the tanks of the casting machine, usually the one containing thesoftening bath, so that here again no additional operation or equipmentis needed. Moreover, resin-containing non-fibrous cellulosic sheetsprecipitated from an aqueous alkaline solution or dispersion andthereafter coated with a cellulose derivative or ether resin topcoat,preferably a moistureproofing coating comprising a cellulose derivativeor ether resin, a wax or wax-like material, a blending agent and aplasticizer, constitute coated sheets the surface coating of which iswell anchored to the cellulosic sheet and adheres to it tenaciousiy forsubstantial periods of time when in direct contact with water or whenused as a wrapping directly in contact with products having a high wateror moisture content such as butter, cheese, wet or frozen fish, icecream or the like. These coated sheets, in which the anchoring effect isachieved by the presence of a synthetic resin in the cellulosic sheet,have the additional advantage of being free of odor. Furthermore, theuncoated non-fibrous cellulosic sheets containing a synthetic resin,made according to this invention, have various uses in themselves.Regenerated cellulose sheets so prepared differ from ordinaryregenerated cellulose sheets with respect to surface deformation etcetera and are therefore peculiarly suited for certain types of printingand embossing, for instance, and for numerous other uses which will atonce suggest themselves.

The following examples illustrate modes of anchoring coatings to basesby incorporating synthetic resins or resin-forming materials into thesolution from which the base is cast.

Example XI.The resin incorporated in the cellulosic sheet as ananchoring medium is prepared by condensing dihydroxydiphenyl propane andformaldehyde in alkaline solution at room temperature and isolating theviscous liquid resulting upon acidification of this solution. Forexample, one molar equivalent of dihydroxydiphenyl propane (M. P. 157C.) is dissolved in an aqueous alkaline solution containing 2 molarequivalents of sodium hydroxide; 3.25 molar equivalents of commercialformaldehyde 137%) are added and the clear solution is allowed to standfor 2 days at room temperature. The mixture is then acidified and theviscous, practically colorless liquid which separates is washed acidfreeand dried in a vacuum oven. This viscous liquid is a resin which is onlypartially condensed, polymerized or hardened and requires furtherheating to complete its condensation, polymerization or hardening. It isnow dissolved in 10 per cent sodium hydroxide to form a solutioncontaining a known weight of 'resin which will preferably range from toper cent by weight.

A sumcient quantity of sodium hydroxide solution of the resin is addedto a solution or viscose containing TV-2% cellulose so that the resinent in the cellulosic sheets formed from the viacose solution will beabout 10% of the total solids in the sheet. After thorough mixing 0! theresin solution in the viscose and deaeration oi the resulting mixturethe resin-containing viscose is cast into sheets in the usual manner.These sheets are washed, bleached and washed again and then led throughan aqueous solution containing 4 per cent by weight 01' dimethylol urea.The excess solution is removed from the sheet by squeeze rolls so thatthe sheet subsequently contains between 3 and 4 times its weight ofsolution and the sheet is then dried at temperatures between 65 and C.by passing it over heated rolls. After being cooled and humidified thesheet is coated with a moistureprooflng composition of the followingformula:

Per cent Nitrocellulose 5.21 Gum dammar 3.22 Dibutyl phthalate 2.30Paraflin (M. P. 60-61 C.) 0.88 Zinc stearate 0.10 Ethyl acetate 45.76Toluene 35.63 Ethanol 6.23 Acetone 0.67

The cellulosic sheet is passed through this bath. the excess bathremoved by a suitable scraping mechanism and the sheet dried at atemperature above the melting point of the wax in the moistureproofingcomposition. After drying the moistureproof coated celiulosic sheet isagain cooled and humidified if necessary to the desired moisturecontent.

Example XII.A suflicient quantity of the resin described in Example XIis dissolved in a viscose solution so that the cellulosic sheets formedfrom the solution contain about 10 per cent of the resin based on thesolid content of the sheets. After thorough mixing and deaeration theresincontaining viscose is cast into sheets, bleached and washed free ofimpurities in the usual manher and dried at temperatures between 65 and95 C. After being cooled and humidified, the sheet is coated with acomposition comprising essentially a wax or wax-like material and theether resin resulting from the reaction of dihydroxydiphenyl propane andB,B'-dichlorodiethyl ether in alkaline solution. The excess coatingcomposition is removed from the sheet by scraping or any suitable meansand the sheet is dried at a temperature above the melting point of thewax employed in the coating composition.

Example XIII .In place of the ether resin used in Example XI, aphenol-formaldehyde resin marketed under the designation, Liquid Durez550, is added to the viscose solution in the same amount and exactly thesame procedure followed throughout as in Example XI.

Example XIV.As an anchoring medium an incompletely polymerized resin 01the glyptal type made by the reaction of glycerol, glycol and adipicacid is incorporated in the cellulosic sheet in the manner described inthe preceding examples by dissolving in the viscose sunicient resin toform 15 per cent of the total solids in the finished cellulosic sheetand before drying passing the sheet through a 4 per cent by weightaqueous solution of dimethylol urea. The finished, dry cellulosic sheetthus prepared is coated with a presmoistureprooilng compositioncomprising a solution of nitrocellulose, paramn, gum damar and dibutyiphthalate.

It will be seen from a study of the various alternative methodsdescribed under the headings A", 3" and "(7 above that the presentinvention may be applied with great efliciency and economy to theproduction of composite films in which the surface coating is securelyanchored to the base so as to withstand the destructive action oi largeamounts 01' water or moisture for prolonged periods or time. Inparticular, moistureproof films made from regenerated cellulose and thelike by coating processes, having a high degree of resistance todeterioration when under the influence of large amounts of water, areproduced in accordance with the principles oi this invention.

It will be understood that the various details involved in the precedingdiscussion 0! the invention may be modified in a number 0! diii'erentways. Any variation or modification, however, which conforms to thespirit of the invention is intended to be included within the scope o!the claims.

We claim:

1. A wrapping tissue comprising a transparent, non-fibrous, celiulosicbase sheet, a transparent moistureprooi coating on said base sheet, atransparent anchoring medium between said base sheet and saidmoistureproot coating. said anchoring medium comprising a syntheticresin taken from the class consisting of a phenol-aldehyde resin and aurea-aldehyde resin which is substantially unafl'ected by water and thesolvents used in the moistureprooi coating.

2. A wrapping tissue comprising a transparent, non-fibrous, cellulosicbase sheet, a transparent moistureprooi coating on said base sheet, atransparent anchoring medium between said base sheet and saidmoistureprooi coating, said anchoring medium comprising a syntheticresin taken from the class consisting of a phenol-aldehyde resin and aurea-aldehyde resin which is substantially unaifected by water and thesolvents used in the moistureprooi coating, said anchoring medium beingincorporated throughout the body of the base sheet. A

3. A wrapping tissue comprising a transparent, non-fibrous, cellulosicbase sheet, a transparent moistureproof coating on said base sheet, atransparent anchoring medium between said base sheet and saidmoistureprooi' coating, said anchoring medium comprising a syntheticpolyhydric phenol-aldehyde resin which is substantially unafieeted bywater and the solvents used in the moistureprooi' coating.

4. In a process for producing a transparent, anchored, moistureproo!wrapping tissue the steps comprising applying an anchoring mediumcomposed oi a synthetic resin taken from the class consisting of aphenol-aldehyde resin and a ureaaldehyde resin on a transparent,non-fibrous, cellulosic base sheet, and applying a transparentmoistureproof coating on said anchoring mediumcontaining base sheet,said resin, in the finished wrapping tissue, being transparent andsubstantially unaii'ected by water and solvents used in themoistureprooi coating.

5. In a process tor producing a transparent, anchored, moistureproofwrapping tissue, the steps comprising applying an anchoring mediumcomposed of a synthetic, polyhydric phenol-aldehyde resin on atransparent, non-fibrous, cellulosic bale sheet, and applying atransparent moistureprooi coating on said anchoring medium-containingbase sheet, said resin in the finished wrapping tissue, beingtransparent and substantially unailected by water and solvents used inthe moistureprooi coating.

6. In a process for producing a transparent, anchored, mcistureprooiwrapping tissue, the steps comprising dissolving a resin-formingmaterial taken from the class consisting of a phenolaldehyderesin-forming material and a ureaaldehyde resin-forming material in anaqueous solution, applying said solution of resin-forming materialsen's. transparent, non-fibro cellulosic base sheet, converting saidresin-taming materials to a transparent, insoluble resin, and applying atransparent, moistureprooi coating on said resin-treated base sheet.

'1. In a procea i'or producing a transparent, anchored, moistureprootwrapping tissue the steps comprising dissolving a phenol and an aldehydein an aqueous solution. applying said solution of a phenol and analdehyde on a transparent, nonflbrous, cellulosic base sheet, convertingsaid phenol and aldehyde to a transparent, insoluble resin, and applyinga transparent, moistureproo! coating on said resin-treated base sheet.

8. In a process for producing a transparent, anchored, moistureprooiwrapping tissue the steps comprising dissolving a carbamide and anaidehyde in an aqueous solution, applyi said solution of carbamide andaldehyde on a transparent, non-fibrous, cellulosic base sheet,converting said carbamide and aldehyde to a transparent, insolubleresin, and applying a transparent. moistureprooi coating on saidresin-treated base sheet.

WILLIAM HALE CHARGE. DOROTHY B. BATELEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,007. May 25, 1939.

WILLIAM HALE CHARCH, ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,first column, line 1,0, for "of water" read or water; same page, secondcolumn, line ?9-L ,O, for "theourea" read thiourea; line 15, for "ase"read as; page 6, first column, line 12, for "formalderyde" readformaldehyde; line 15, for "accordang" read according; same page, secondcolumn, line 6, for "solutoin" read so1ution;'line 1+}, for the word"impossible" read possible; page 7 second column, line 35, for"moisture-proofing" read mois'tureproofing; line 75, for "stick" readsticky; page 9, first column, line 3, after the word "sheet" insertalone, the. cellulosic sheet; and that the said Letters Patent should beread with this correction therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 1 th day of July, A. D. 1959.

Henry Van Arsdale (S l) Acting Commissioner of Patents.

coating on said anchoring medium-containing base sheet, said resin inthe finished wrapping tissue, being transparent and substantiallyunailected by water and solvents used in the moistureprooi coating.

6. In a process for producing a transparent, anchored, mcistureprooiwrapping tissue, the steps comprising dissolving a resin-formingmaterial taken from the class consisting of a phenolaldehyderesin-forming material and a ureaaldehyde resin-forming material in anaqueous solution, applying said solution of resin-forming materialsen's. transparent, non-fibro cellulosic base sheet, converting saidresin-taming materials to a transparent, insoluble resin, and applying atransparent, moistureprooi coating on said resin-treated base sheet.

'1. In a procea i'or producing a transparent, anchored, moistureprootwrapping tissue the steps comprising dissolving a phenol and an aldehydein an aqueous solution. applying said solution of a phenol and analdehyde on a transparent, nonflbrous, cellulosic base sheet, convertingsaid phenol and aldehyde to a transparent, insoluble resin, and applyinga transparent, moistureproo! coating on said resin-treated base sheet.

8. In a process for producing a transparent, anchored, moistureprooiwrapping tissue the steps comprising dissolving a carbamide and anaidehyde in an aqueous solution, applyi said solution of carbamide andaldehyde on a transparent, non-fibrous, cellulosic base sheet,converting said carbamide and aldehyde to a transparent, insolubleresin, and applying a transparent. moistureprooi coating on saidresin-treated base sheet.

WILLIAM HALE CHARGE. DOROTHY B. BATELEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,007. May 25, 1939.

WILLIAM HALE CHARCH, ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,first column, line 1,0, for "of water" read or water; same page, secondcolumn, line ?9-L ,O, for "theourea" read thiourea; line 15, for "ase"read as; page 6, first column, line 12, for "formalderyde" readformaldehyde; line 15, for "accordang" read according; same page, secondcolumn, line 6, for "solutoin" read so1ution;'line 1+}, for the word"impossible" read possible; page 7 second column, line 35, for"moisture-proofing" read mois'tureproofing; line 75, for "stick" readsticky; page 9, first column, line 3, after the word "sheet" insertalone, the. cellulosic sheet; and that the said Letters Patent should beread with this correction therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 1 th day of July, A. D. 1959.

Henry Van Arsdale (S l) Acting Commissioner of Patents.

